The present invention relates generally to underground directional boring, underground resource extraction and more particularly, to automatically extending and retracting electrically isolated conductors provided in a segmented drill string. An associated method is also disclosed.
Guided horizontal directional drilling techniques are employed for a number of purposes including, for example, the trenchless installation of underground utilities such as electric and telephone cables and water and gas lines. As a further enhancement, state of the art directional drilling systems include configurations which permit location and tracking of an underground boring tool during a directional drilling operation. As will be seen, the effectiveness of such configurations can be improved by providing an electrical pathway between a drill rig which operates the boring tool and the boring tool itself.
Turning to FIG. 1, a horizontal boring operation is illustrated being performed using a boring/drilling system generally indicated by the reference numeral 10. The drilling operation is performed in a region of ground 12 including an existing underground utility 14. The surface of the ground is indicated by reference number 16.
System 10 includes a drill rig 18 having a carriage 20 received for movement along the length of an opposing pair of rails 22 which are, in turn, mounted on a frame 24. A conventional arrangement (not shown) is provided for moving carriage 20 along rails 22. During drilling, carriage 20 pushes a drill string 26 into the ground and, further, is configured for rotating the drill string while pushing. The drill string is made up of a series of individual drill string or drill pipe sections 28, each of which includes any suitable length such as, for example, ten feet. Therefore, during drilling, drill pipe sections must be added to the drill string as it is extended or removed from the drill string as it is retracted. In this regard, drill rig 18 may be configured for automatically or semi-automatically adding or removing the drill string sections as needed during the drilling operation. Underground bending of the drill string enables steering, but has been exaggerated for illustrative purposes.
Still referring to FIG. 1, a boring tool 30 includes an asymmetric face 32 and is attached to the end of drill string 36. Steering of the boring tool is accomplished by orienting face 32 of the boring tool (using the drill string) such that the boring tool is deflected in the desired direction. Boring tool 30 includes a mono-axial antenna such as a dipole antenna 44 which is driven by a transmitter 46 so that a magnetic locating signal 48 is emanated from antenna 44. In one embodiment, power may be supplied to transmitter 46 from a set of batteries 50 via a power supply 52. In another embodiment (not shown), to be described in further detail below, an insulated electrical conductor is installed within the drill string between the drill rig and the boring tool in order to carry power to transmitter 46. A control console 54 is provided at the drill rig for use in controlling and/or monitoring the drilling operation. The control console includes a display screen 56, an input device such as a keyboard 58 and a plurality of control levers 60 which, for example, hydraulically control movement of carriage 20 along with other relevant functions of drill rig operation.
Drill pipe 28 defines a through passage (not shown) for a number of reasons, including considerations of design, manufacturing methods, strength, and weight, but also because typical horizontal directional drilling also requires the use of some type of drilling fluid (not shown), most commonly a suspension of the mineral bentonite in water (commonly referred to as xe2x80x9cdrilling mudxe2x80x9d). Drilling mud, which is generally alkaline, is emitted under pressure through orifices (not shown) in boring tool 30 after being pumped through the innermost passage of drill pipes 28 which make up drill string 26. Drilling mud is typically pumped using a mud pump and associated equipment (none of which are shown) that is located on or near drill rig 18. The pressures at which the drilling mud is pumped can vary widely, with a commonly encountered range of operation being 100 PSI to 4,000 PSI, depending on the design and size of the particular drill rig. For proper operation, pipe connections between drill pipe sections 28 must not only be sufficiently strong to join the sections against various thrust, pull and torque forces to which the drill string is subjected, but they must also form a seal so as to not allow the escape of drilling mud from these connections which could result in an unacceptable drop in drilling mud pressure at the orifices of the boring tool.
Continuing to refer to FIG. 1, drilling system 10 may include a portable locator/controller 70 held by an operator 72 for sensing locating signal 48 in a way which allows the underground position of boring tool 30 to be identified. Such portable detectors are described, for example, in U.S. Pat. Nos. 5,155,442, 5,337,002, 5,444,382 and 5,633,589 as issued to Mercer et al, all of which are incorporated herein by reference. Alternatively, one or more detectors (not shown) designed for positioning at fixed, above ground locations may be used, as described in U.S. patent application Ser. No. 08/835,834, filing date Apr. 16, 1997, which is commonly assigned with the present application and is incorporated herein by reference.
Guided horizontal directional drilling equipment is typically employed in circumstances where the inaccuracies and lack of steering capability of non-guided drilling equipment would be problematic. A typical example is the situation illustrated in FIG. 1 in which the intended drill path requires steering the boring tool around, in this instance beneath, obstacles such as utility 14. Guided drilling is also important where the intended path is curved (not shown) or the target destination is more than a short distance (typically over 50 feet) from the starting point. In the latter situation, simply aiming a non-guided boring tool at the target destination from the starting point will seldom result in maintaining a sufficiently accurate drill path and/or arriving reasonably close to the target destination.
While system 10 of FIG. 1 illustrates a xe2x80x9cwalk-overxe2x80x9d type locating system using a steerable boring tool, it should be appreciated that xe2x80x9cnon-walkoverxe2x80x9d guidance/locating systems (not shown) are also useful in conjunction with steerable boring tools. The less commonly used non-walkover systems typically utilize an instrumentation/sensor package (not shown) located in the boring tool that is electrically connected directly to console 54 at the drill rig via the aforementioned insulated electrical conductor (not shown) located inside the through passage of the drill string. While batteries 50 may be used in the boring tool to power the instrumentation/sensor package, the insulated conductor may be used to supply electrical power to the instrumentation/sensor package, thus eliminating batteries 50 for reasons which will be seen. At the same time, data may be transmitted from the instrumentation/sensor package to console 54 on the insulated conductor. Data can also be sent to the instrumentation/sensor package for calibration, signal processing and programming.
In the instance of both walkover and non-walkover systems, the objective is to use information obtained from the locating system as a basis for making corrections and adjustments to the direction of steerable boring tool 30 in order to drill a bore hole that follows an intended drill path. Therefore, in most drilling scenarios, a walkover system is particularly advantageous since the origin of the locating signal leads directly to the position of the boring tool. Typically, the locating signal, in a walkover system, is also used to transmit to above ground locations encoded information including the roll and pitch orientation of boring tool 30 along with temperature and battery voltage readings. Battery powered transmitters often employ one to four replaceable internal xe2x80x9cdry-cellxe2x80x9d type batteries as a source for electric power.
Although internal battery powered transmitters perform satisfactorily under many conditions, there are a number of limitations associated with their use, most of which are due to the relatively low electric power available from dry-cell batteries. For example, battery life for a self-powered transmitter is relatively short and, under some circumstances, the exhaustion of batteries can result in the need to withdraw an entire drill string for the purpose of replacing batteries in order to complete a drill run. It should also be appreciated that the low power level available from dry-cell batteries, from a practical standpoint, limits the signal strength of locating signal 48. The available signal strength is of concern in relation to the depth at which the boring tool may be tracked. That is, the above ground signal strength of locating signal 48 decays relatively rapidly as depth increases. The maximum operating depth for reliable receipt of locating signal 48 using a dry-cell powered transmitter 46 is limited to approximately 100 feet, depending on the particular design and characteristics of boring tool transmitter 46 and the above ground detector(s) used. This distance may decrease in the presence of passive and active forms of magnetic field interference, such as metallic objects and stray magnetic signals from other sources.
As a result of these limitations, drill head transmitters for walkover systems have been developed that can be powered by an above ground external power source via the aforementioned electrical conductor. That is, the typical electrical conductor for this external power source is similar to that used with non-walkover systems, namely a single insulated wire that connects to the transmitter with the ground return for the electrical circuit including the metallic housing of boring tool 30, drill pipe 28 making up the drill string, and drill rig 18. Even in the case where a locating signal is transmitted from the boring tool, the electric conductor may be used to send information from boring tool 30 to the drill rig including, for example, the roll and pitch orientation of the boring tool, temperature and voltage, using a variety of data encoding and transmission methods. By using the insulated electrical conductor, reliable operational depth may be increased by increasing the output power of transmitter 46 without concern over depletion of internal battery power. Moreover, information encoded on the electrical conductor can be received at the drill rig essentially irrespective of the operating depth of the boring tool and background noise level.
The prior art practice (not shown) for using externally-powered electronic and electrical devices located in the boring tool has been to insert a piece of insulated electrical conducting wire of appropriate length inside each piece of drill pipe 28 and manually perform a physical splice of the electrical wire to the wire in the prior section of drill pipe 28 each time an additional drill pipe section is added to the drill string. The process typically entails the use of specialized and relatively expensive crimp-on connectors and various types of heat-shrinkable tubing or adhesive wrappings that are mechanically secure, waterproof, and resistant to the chemical and physical properties of drilling mud. The process of interrupting pipe joining operations to manually splice the electrical conductor is labor-intensive and results in significant reductions in drilling productivity. Care must also be taken by the person performing splicing to avoid twisting or pinching the electrical wire, and any failure to properly splice can result in wire breakage and the need to withdraw the drill string to make repairs. For drill rigs having the capability of adding/removing drill pipe automatically or semi-automatically, this otherwise useful time and labor saving function must be disabled or interrupted to allow a manual splice of the electric wire. After completing the drill run, a reverse process of withdrawing the drill string and removing each section of drill pipe 28 from the ground requires cutting the wire each time a section of drill pipe is removed, resulting in considerable waste due to the discard of these once-used electrical wires and splicing materials.
Electrical conductors have been described by the prior art for use in applications other than horizontal directional drilling. One specific field of application resides in extraction of underground resources such as, for example, oil and natural gas. The need for an electrical communication path arises, in many instances, for the purpose of monitoring, controlling and/or providing operational power to in-ground devices such as valves and data acquisition modules. One such approach is exemplified by U.S. Pat. No. 6,257,332 entitled WELL MANAGEMENT SYSTEM (hereinafter the ""332 patent). The problem being solved may be different, in some instances, than that encountered with respect to HDD, however, since HDD drill strings generally rotate. The objective, in the instance of a pre-existing wellbore such as an oil or gas well, may be to install an electrical cable in a pre-existing wellbore. Thus, a drill string type arrangement may simply be dropped or pushed into the pre-existing wellbore without the need for rotation or actual drilling. In this regard, the ""332 patent and its related background art contemplates simply attaching an electrical cable to the exterior of the drill string as it is extended into the wellbore or, alternatively, threading the cable through the interior passage of the drill string. This latter approach is quite inconvenient unless a continuous (i.e. non-sectioned) pipe is used to house the cable since a cable splice must generally be performed whenever additional pipe is added to the drill string. Where the cable is attached to the exterior of the drill string, it is so exposed as to quite readily be damaged in any number of situations. As one example, the cable may be crushed between the drill string and the casing of the wellbore. As another example, the need even for limited rotation of the drill string such as for the purpose of steering could cause the cable to detach from the drill string. It should be appreciated that either type of cable installation is primarily possible due to the general non-rotation of the drill string.
The present invention provides a heretofore unseen and highly advantageous arrangement and associated method which automatically forms an isolated electrically conductive pathway between a drill rig and boring tool as the drill string extending between the drill rig and the boring tool is either extended or shortened.
As will be described in more detail hereinafter, there are disclosed herein arrangements and an associated method of providing an isolated electrically conductive path in a system in which a boring tool is moved through the ground in a region. The system includes a drill rig and a drill string which is connected between a boring tool, or other in-ground device, and the drill rig and is configured for extension and/or retraction from the drill rig such that, when the drill string is extended, the boring tool moves in a forward direction through the ground and, when the drill string is retracted, the boring tool moves in a reverse direction approaching the drill rig. The drill string is made up of a plurality of electrically conductive drill pipe sections, each of which includes a section length and all of which are configured for removable attachment with one another to facilitate the extension and retraction of the drill string by one section length at a time. The improvement comprises an arrangement associated with each drill pipe section for providing part of at least one electrically conductive path along the section length of each drill pipe section, which electrically conductive path is electrically isolated from its associated drill pipe section and extends from the boring tool to the drill rig such that the electrically conductive path is extended by the section length when the drill string is extended by attachment of an additional drill pipe section to the drill string at the drill rig and the electrically conductive path is shortened by the section length when the drill string is shortened by detaching the additional drill pipe section from the drill string at the drill rig.
In one aspect of the present invention, a system is disclosed including a drill string for at least partial use in the ground. The drill string includes a length which is extendable and/or retractable through being made up of a plurality of pipe sections having opposing first and second ends and a section length defining an innermost passage and all of which pipe sections are configured for removable attachment with one another by physically connecting the first end of one pipe section with the second end of another pipe section to facilitate extension of the drill string by one section length at a time in a way which aligns the interior passage of attached ones of the pipe sections. As a portion of the system, an assembly is provided for use with each of the pipe sections including a pair of adapters for installation of a first one of the adapters in a first end of the innermost passage of each one of the pipe sections and installation of a second one of the adapters in a second end of the innermost passage of each one of the pipe sections. The first adapter defines a first electrical contact area and the second adapter defines a second electrical contact area. The first and second adapters are configured for resiliently biasing the first and second contact areas against one another between attached ones of the pipe sections to establish an electrical connection between the pair of adapters. An electrically conductive arrangement is located in the innermost passage of each pipe section and extends between and electrically connects each one of the pair of adapters so as to provide an electrically conductive path interconnecting the pair of adapters of each pipe section in electrical isolation from the pipe sections and cooperating with the adapters to form an electrically isolated path through the drill string.
In another aspect of the present invention, the first one of the pair of adapters is configured to resiliently bias the first electrical contact area against the second electrical contact area defined by the second adapter to provide electrical contact between the first and second electrical contact areas while adjacent ones of the pipe sections are attached to one another.
In still another aspect of the present invention, the first adapter includes a first electrically conductive member having a resilient section including a free end defining the first electrical contact area and having an opposing end configured for electrical communication with the electrically conductive arrangement. The free end is configured for engaging the second adapter in a way which brings the first and second electrical contact areas into electrical contact as adjacent ones of the pipe sections are attached to one another and, thereafter, resiliently biases the first electrical contact area against the second electrical contact area. In one feature, the first adapter is configured to apply a resilient bias in a direction generally along the length of the drill string between attached ones of the pipe sections to bias the first electrical contact area against the second electrical contact area. In another feature, the first adapter includes a first electrically conductive member having a resilient section including a free end defining the first electrical contact area and having an opposing, first connection end for electrical connection to the electrically conductive arrangement with a first conductive length defined between the first connection end and the resilient section. The first connection end is supported within the innermost passage of its associated pipe section with the resilient section extending outwardly from the innermost passage. In still another feature, the first conductive member is integrally formed using a resiliently flexible electrically conductive material. In yet another feature, the resilient section is in the form of a helical compression spring defining an axis generally oriented along the axis of the drill string. In a further feature, the first electrical contact surface is defined on the free end of the first conductive member facing away or outwardly from each pipe section in which the first adapter is installed.
In a further aspect of the present invention, the first and second adapters, along with the electrically conductive arrangement, may be installed in pipe sections in conjunction with the manufacturing process of the pipe sections. Alternatively, the first and second adapters may be provided as an after market kit for use with pipe sections already in field use.
In a continuing aspect of the present invention, one or more drill strings configured in accordance with the present invention so as to define an electrically isolated conductive path may be used as part of an electrical communication and/or power supply arrangement installed, for example, in a well in a way which forms a multiplexed data and power supply network. Such drill strings may be used, for instance, in horizontal directional drilling or in underground resource extraction.